Filter element

ABSTRACT

The invention relates to a filter element for fluid filtration, in particular for hydraulic fluid, consisting of element components, such as a preferably pleated and multi-layer filter material (10) that extends between two end caps (26) and at least partially comprises a fluid-permeable supporting tube (14) forming a hollow cylinder, characterized in that at least one element component of the filter element is provided at least partially with at least one luminescent material or another marker in such a manner that said material or marker is excited to a characteristic, detectable wave emission when exposed to a certain exciter wave or wave spectrum.

The invention concerns a filter element for fluid filtration, inparticular for hydraulic fluid, comprised of element components such asa preferably pleated multi-layer filter material that extends betweentwo end caps and which at least partially comprises a fluid-permeablesupporting tube forming a hollow cylinder.

Filter elements of this kind are readily available on the market in aplurality of designs. Such filter elements, as they are described forexample in DE 10 2004 061 078 A1 and EP 0 001 407 B1, are designed to beinserted into a filter housing for the purpose of cleaning dirty fluid,for example in form of a hydraulic medium, through the inserted filtermaterial of the filter element, and to return the thus cleaned fluidfrom the filter housing back into the fluid circuit, in particular ahydraulic fluid circuit. If after a plurality of filter cycles thefilter material is blocked with dirt to the degree that it is unusable,the filter element is removed from the housing and replaced by a newelement.

To increase the filtering surface, the filters are usually made of astar-like folded or pleated strip of filter mat, which concentricallysurrounds an internal and/or external supporting tube in a circularmanner, which the filter material with its in cross-section star-likearranged filter pleats is able to brace against depending on flowdirection. To that extent it is also possible to reverse the filtrationdirection so that reverse flushing actions with already cleaned fluidare possible, and that in his way a filter material that is clogged withcontaminating particles can be cleaned. The filter material as such hasa multi-layer mat structure, and the respective layer arrangement isdependent on the required filtration task. Nevertheless, layerarrangements are often used that have purely filtering or draininglayers that are made from native fibres, glass fibres, metal fibrematerial and synthetic fibres such as meltblown fibres, carbon fibresand so on. To ensure the secure adherence of the layers to each other itmay also be provided that the two cover layers of the filter materialare made from a finely woven synthetic or wire fabric as the respectivesupporting fabric, which also prevent the washing out of fibre materialduring operation of the filter element.

The disadvantage of such filter elements, which are on the market inmany different forms and designs and which are widely used, for example,in hydraulic systems where hydraulic oil flows through system branches,is that they are often on the market as counterfeit products withoutguaranteed characteristics and labelling. Furthermore, often low-qualitycounterfeit products appear on the market that bear the original companylogos and manufacturer's details and thus obscure the facts and misleadconsumers regarding the actual source of the filter element product.

With specified filter characteristics such as differential pressurestability, beta stability, filter fineness in conjunction with purityclass, dirt absorption capacity, long-term service characteristics andsuch like, many different hydraulic-related filter task can be met ifand as long as original filters from reputable manufacturers are usedand not low-quality counterfeit products that usually come from low-wagecountries and illegally enter the world-wide market.

Due to increased quality requirements, which are also the result of thecomplexity of modern machines and plants that operate with hydrauliccomponents, it is indispensable that, for the specified filter task, thefilter element used is preferably designed specifically for the requiredfilter characteristic, in particular in the instance where theapplication of the filter element fluid filtration involves asecurity-related technology, the breakdown or malfunction of which couldlead to serious damage of machines and/or injury to persons.

This danger is always present where counterfeit products or technicallyinferior copies are used that do not come with reliable productinformation and which, due to the illegal use of company details such aslogos and company names, are erroneously attributed to the originalmanufacturer, who may then be held accountable by the operator for thedamage done to machines and plants caused by the counterfeit product.

Based upon the above described problem it is the object of the inventionto provide the manufacturer of the filter element with a tool thatenables him to identify elements already supplied and in use as his own,even if counterfeits products have been made by third parties. Moreover,if required it is made possible for the manufacturer to receiveinformation about the supplied filter element on site. This object isachieved by a filter element with the characteristics of claim 1 in itsentirety.

Since, according to the characterising part of claim 1, at least oneelement component of the filter element is at least partially providedwith a luminescent or other marker in such a manner that said materialor marker is excited to a characteristic, detectable wave emission whenexposed to a certain exciter wave or wave spectrum, installation orservice personnel sent by the original manufacturer is able to reliablydetermine on site, that is, at the location of use of the respectivefilter element, whether this filter element product originates from themanufacturer or not. Said assessment on site may be able to be made withthe naked eye; it is, however, preferred to provide a specificallyadapted acquisition and evaluation unit that makes the luminescentmaterial or marker provided on the filter element recognisable to anobserver.

Should the luminescent material or other marker have been provided bythe manufacturer with readable information, the information read out onsite can be used to again obtain said technical information, for examplewhich manufacturing series this element comes from, when and in whichplant it had been manufactured, what filtration characteristics areinherent in the element material, etc. Based upon this technicalinformation it is possible, in case of malfunction and provided that itreally is an original element of the manufacturer, to change theproduction of such elements in such a way that any malfunctions areavoided in future. Since this is a completely new method for elementidentification and assessment, it is impossible from today's point ofview to foresee all possible applications and uses of the invention. Thesolution according to the invention has therefore no parallel in theprior art.

In a preferred embodiment of the filter element according to theinvention the luminescent material or other marker is of an organicnature and is provided in form of a fluorescent material, comprising atleast a host lattice and an activator that is preferably present inionic form, which is responsible for the emitted wave image, inparticular in form of light. Due to the use of a fluorescent material aparticularly good identifiability of the element information to be readout is assured, so that a reliable identification is achieved even ondifficult to access machine and plant parts in a dark environment.

Moreover, it is preferable that the host lattice is made from oxidicmaterials, preferably Y₂O₃ or Lu₃Al₅O₁₂, and that the materials used asactivators are preferably rare earths and/or transition metals such asmanganese, chromium or iron. Particularly when using rare earths, whichare relatively expensive on the market, it is advantageous to introducethem in ionic form into the host lattice since the small quantity ofrare earths keeps the cost down. Since users consider filter elementsonly as low-cost consumables, the identification system according to theinvention must not be too costly so as not to increase the overall priceto the user significantly.

If oxidic materials are used for the host lattice it is possible to makethe host lattice very stable and abrasion-resistant for the activatorthat causes the actual fluorescence, so that in the rough day-to-dayoperation of the filter element the marking characteristic of theactivator is not accidentally diminished.

In a further preferred embodiment of the filter element according to theinvention provision is made that, in order to achieve a strongreflection on the surface of the respective element component,short-wave, in particular ultraviolet (UV) light is used, and for deepermaterial layers that are located below the surface, long-wave light, inparticular infrared (IR) light is used. In order to analyse these typesof luminescent materials, light spectroscopy is particularly suitable,since all sections of the light spectrum, such as the UV/VIS/IR spectrescan be detected reliably.

The very short-wave identification light that is used, which isinvisible to the human eye, is partially absorbed and re-emitted by theluminescent material or marker used. This results in long-wave lightbeing reflected, which is directly visible to the human eye. Analternative possibility is that short-wave light is reflected that isnot visible to the human eye but which is verified specifically by meansof a spectroscopy method.

The particle size of the luminescent material pigments is preferablyless than 1 μm so that said pigments can easily be mixed into adhesivesor inks to ensure that even a small amount of mixed-in pigments makes areliable later identification of the filter element possible. At leastpurely mathematically it is possible to generate in this manner 300billion combinations of unique “fingerprints” that are still clearlydistinguishable in their spectral behaviour, so that it becomes almostforgery-proof and impossible for the counterfeit producer to copy thespecial fingerprint that is applied by the original manufacturer. Thismakes it possible to ensure a reliable differentiation between theoriginal and the counterfeit product on site, and thus also by the userof the product.

As already described, the fluorescent material used for the marking offilter elements is provided as a kind of ink, or it is in an adhesive,preferably mixed into a single or multiple-component adhesive, withwhich the individual element components may at least partially beconnected to each other and form the filter element.

The adhesive that contains the fluorescing material serves preferably toattach the filter mat ends of the filter material to each other and/orto attach the end of the filter material to at least one of the end capsof the filter element.

The individual filter folds of the pleated filter material are spacedand fixed in the adhesive bed of the end cap of the filter element insuch a way that a direct optical or other sensoric recognition of partsof the respective adhesive bed with the infused marker between adjacentfilter folds is possible.

A further possibility for marking the components that are used in themanufacture of filter elements, for example the plastic (PET) sleeve asthe outer supporting tube cover, the end caps, the O-rings as seals, thebypass valve or the filter material itself can take place in that aspecial tincture that is comprised of ink in which luminescent materialis suspended or dispersed, is applied as fluorescent marker. Theapplication may be in form of a printing method, for example through padprinting, so that also uneven surfaces can be printed on. There is alsothe possibility of mixing the luminescent or marker material directlyinto the adhesive or the elastomeric material with which the componentsare manufactured.

Beside the ink as carrier for luminescent materials, single-component ortwo-component epoxy resins and polyurethane are also suitable. In thesame manner it is possible to use other chemically curing adhesives thatcure according to the principle of polyaddition, polycondensation orpolymerisation to a thermoset, thermoplast or elastomer. All adhesivescan be processed as single-component or two-component variations andinfused with fluorescent markers. The fluorescent marker as luminescentmaterial is dispersed or suspended in the adhesive and is permanentlyembedded in the adhesive material through cross-linking and curing ofthe adhesive, so that the marking remains intact even after a longstorage period and over many operating hours.

Moreover, the invention may also be implemented using a physical curingadhesive.

Further details of the invention are now described in more detail by wayof an exemplary embodiment in conjunction with the respective drawings.

Shown in principle and not to scale are in:

FIG. 1 a partial cross-section, partially in perspective, one end of afilter element;

FIG. 2 a cross-section through the filter element shown in FIG. 1;

FIG. 3 the emission spectrum of an emitted, individual light spectrum ofa marker after excitation through UV light;

FIG. 4 the arrangement of fluorescent markers in a two-component epoxyresin;

FIG. 5 the arrangement of fluorescent markers in a single-componentepoxy resin; and

FIG. 6 the arrangement of fluorescent markers in a two-componentpolyurethane material; all of the above-named fluorescent markers areshown symbolically as circles or points, where each circle or pointcorresponds to a host lattice with embedded activators.

Details of the invention are now described in more detail by way ofexemplary embodiments in conjunction with the above-mentioned drawings.

The filter element, of which the upper half is depicted in FIG. 1 andwhich is part of the prior art (DE 10 2004 061 078 A1), features asfilter component a filter mat 10 with a defined surface area and definedfilter characteristics. Said filter mat may be formed as a cylinder (notshown) or, as depicted in FIG. 1, may be folded or pleated withindividual filter folds 12, which extend tightly packed between aninner, fluid-permeable supporting tube 14 and an outer cylindricalhousing mantle, or supporting tube casing 16 respectively, which is alsofluid-permeable. The individual filter folds 12 are shown partiallypulled apart to make the illustration clearer, where the individuallayer structure of the pleated filter mat 10 becomes apparent from thepartial depiction that faces the viewer.

In filter elements of this design the filter mat 10 consists usually ofa first layer as the supporting fabric 18, a second layer 20 asprotection fleece, a third layer 22 as main fleece, possibly a furthernot-depicted layer of a subsequent protective layer, and certainly afourth layer 24 of another supporting fabric 24 that extends around theinner circumference. Said supporting fabrics 18, 24 may be made from awire fabric, a plastic mesh or a plastic fabric. The protection fleecelayers 20 are usually made from a synthetic fleece, and the main fleecelayer 22 consists of materials such as glassfibre paper, syntheticfilter material (meltblown fibres) as well as cellulose paper. Saidlayers may also be assembled from composite materials of the same ordifferent kind. This structure is commonly used for hydraulic filterelements and thus does not require a more detailed description.

The filter mat 10 as filter component has, depending on its layerstructure and the filter materials used, defined filter characteristicswhich are guided by the filtration task to be achieved. The basicrequirement here is a high differential pressure stability as well as ahigh beta stability across a wide differential pressure range, definedfilter fineness for all purity classes, large dirt absorption capacitiesas well as a long service life and a small physical size if required.

Looking at FIG. 1, the flow direction in the known solution through thefilter mat 10 is from outside to inside and is braced at its innercircumference with its folding edges against the outer circumference ofthe plastic supporting tube 14 with its annular fluid ports. Each of thefilter mat ends is received by an end cap, where FIG. 1 shows the upperend cap 26 only, and said filter mat end is received in an adhesive bed27 inside end cap 26 and is solidly attached thereto. Moreover, saidupper end cap 26 comprises a spring-loaded bypass valve 28, which allowsfluid to pass for safety reasons even if the filter mat 10 is caked withdirt or blocked respectively.

As is apparent from the cross-sectional diagram of the filter elementaccording to FIG. 2 and seen in circumference direction of the pleatedfilter mat 10, the two free longitudinal end edges 30, 32 are broughttogether by a U-shaped longitudinal seam clip 34, and the connectionbetween longitudinal seam clip 34 and the two longitudinal edges 30, 32is ensured through an adhesive bed 35. This design is commonly used andis described in detail in the prior art in form of EP 1 409 106 B1. Therespective bonding of the adhesive beds 27 and 35 is achieved throughthe use of an adhesive that contains fluorescent particles, where therespective adhesive bed 27, 35 takes the form of a casting compound andestablishes the connection of the filter mat 10 with the respective endcap 26 as well as the connection of the free longitudinal edges 30, 32to each other by means of the longitudinal seam clip 34. Moreover,filter element solutions are possible in which the bonding of thelongitudinal edges 30, 32 can take place without the longitudinal seamclip 34 (not shown). Basically, single or two-component adhesives may beused as bonding agents; moreover, a physical curing adhesive may also beused to achieve that.

The FIG. 4 depicts an example of a two-component epoxy resin(2-component system), where the resin contains diepoxides orpolyepoxides on the basis of bisphenol A novolacs®, and the curingagents used are polyamines, thiols as well as anhydrides. The adhesiveis cured through polyaddition, which results in a duromer after curing.The fluorescent markers are then integrated into this two-componentepoxy resin base structure, symbolically shown in form of points orcircles respectively in the epoxy resin.

FIG. 5 shows the example of a one-component epoxy resin (one-componentsystem) as suitable adhesive for the embedding of the fluorescentmarkers, where said resin is basically formed from a carboxylic acidanhydride and an epoxy resin chain with hydroxyl groups. FIG. 6 incontrast shows as example a two-component polyurethane system(two-component system) based on hexamethylene diisocyanate with1,4-butylene glycol. The fluorescent markers embedded into the adhesivebase are also shown in FIGS. 5 and 6 symbolically as points and circlesrespectively.

To obtain the respective fluorescent marker, fluorescent substances areused that are mainly formed from elements of “rare earths”. These arelisted under the numbers 21, 39 as well as 57 to 71 in standard periodictables. Said substances have a fluorescent effect through excitationwith a certain light wave spectrum, for example UV light. The organicluminescent material as a whole, which is used as fluorescent marker,consists of a host lattice as well as activator ions that areresponsible for the emitted light. Suitable as host lattice are mainlyoxidic materials, such as Y₂O₃ or Lu₃Al₅O₁₂, for example due to theirhigh stability. The usual activators that are used are the alreadymentioned rare earths as well as transition metals such as manganese,chromium or iron. The fluorescent marker that may be specifically formedthis way is represented symbolically in FIGS. 4 to 6 by points orcircles.

If the above-mentioned fluorescent substances, which could be calledluminescent material pigments, are irradiated with short-wave light thatis invisible to the human eye, said light is partially adsorbed andreemitted. The fluorescent marker arrangement may be chosen such thatthe short-wave light is reflected as long-wave light by the carrier ofthe fluorescent marker, which can be seen directly by the human eye.Alternatively it is possible that the irradiated, short-wave light isalso reflected as short-wave light, which cannot be seen by the humaneye but can be detected with analysis and evaluation units based onspectroscopy.

An example of such an emission spectrum of specially developedfluorescing substance (fluorescent marker) is shown in FIG. 3, which isembedded in the adhesive according to one of the above describedsystems. FIG. 3 shows the intensity I of the light reflected from thefluorescent marker over the wavelength λ. As is apparent from the peakrepresentation in FIG. 3, a significant reflection marker is set, forexample, at 700 nm so that, based on the measured emission spectrum, thefilter element product that has been marked with the fluorescent markercan be easily identified as an original product. In the same manner aproduct may be recognised as counterfeit because it does not have suchan emission spectrum, or is marked with one that has a differentlyshaped peak.

The basic principle is that every fluorescent substance emits anindividual light spectrum after excitation through a light source, forexample UV light. Although not detectable by the human eye, the emissionspectrum shown in FIG. 3 can be verified with the aid of stationaryspectroscopy equipment in a laboratory, but also on site using portableequipment. Received spectra in the ultraviolet range, in the infraredrange and in the visual range can, moreover, be digitised and can becompared to the manufacturing data of the manufacturer held responsibleby means of suitable communication facilities.

With spectroscopic methods it is possible to analyse the characteristicspectrum and to receive an unambiguous identification that is comparableto a genetic fingerprint. Since it is possible to mix variousfluorescing substances and thus generate new fingerprints throughsuperimposition of the reflected wave emission, recreating the resultingindividual emission spectrum by a counterfeit manufacturer is hardlypossible so that the described identification system is to be consideredforgery-proof. Moreover, it is possible to also generate in the samemanner technical information via the fluorescent marker, which can thenbe read out to receive additional information, for example concerningthe manufacturing location and method of the filter element thus marked.

The fluorescent marker used is also forgery-proof due to the fact that,for example, the type, the origin, the purity but also the particle sizeof the raw materials used plays a significant role in the manufactured,unique emission spectrum. Also the method of manufacturing theluminescent material pigments, for example based upon sol-gel processes,or the type of a solid-state reaction has an effect on the resultingcharacteristic emission spectrum, just like the production temperature,for example, the heating time or the kind of crucible used, whichincreases the security from unwanted forgeries through counterfeitmanufacturers. Since the individual filter folds 12 of the filter mat 10are spread open in the respective end cap 26 and retained through theadhesive bed 27, it is possible to gain direct optical access fromoutside to view the respective fluorescent marker used. This appliesalso in the instance where the longitudinal filter edges 30, 32 with theadhesive bed 35 are connected to each other and sealed with suitablefluorescent markers. The marking may be placed on the filter element indiscrete, selected places, which makes it difficult to find for apotential forger and also contributes to the level of security.

Further locating options are to mix the respective fluorescent markerinto the synthetic materials of end caps 26, longitudinal seam clips 34,components of a bypass valve 28 and similar. Another possibility is tomix the respective fluorescent marker also into the elastomer materialof seals, for example in form of O-rings (not shown). Since thefluorescent markers can not only be mixed into an adhesive and/orsynthetic material, but can also be applied to the element as afluorescent ink, for example in form of pad printing or a roll-onprocess, it is possible to apply the respective marker on these filterelements as part of the labelling process on the outer housing mantle16, for example. Moreover, it is also possible to embed the fluorescentmarker also into the layers of the filter mat 10.

As already mentioned, depending on the pigment used which, for example,is invisible to the human eye, potential counterfeit producers may noteven know that the filter element is provided with copy protection atall. Considering the plurality of possible application locations, asdescribed above, it is difficult for a forger to even search for thecopy protection in the correct location. But even if this location isfound, due to the complexity of the emission spectra available to choosefrom and to construct, it is difficult for the forger to emulate thecopy protection.

In summary it can be said that with the above described filter elementsolution an effective copy protection system is achieved that iseconomical to implement. This has no parallel in the prior art.

1. Filter element for fluid filtration, in particular for hydraulicfluid, comprised of element components such as a preferably pleatedmulti-layer filter material (10) that extends between two end caps (26)and which at least partially comprises a fluid-permeable supporting tubeforming a hollow cylinder (14), characterised in that at least oneelement component of the filter element is at least partially providedwith at least one luminescent or other marker in such a manner that saidmaterial or marker is excited to a characteristic, detectable waveemission when exposed to a certain exciter wave or wave spectrum. 2.Filter element according to claim 1, characterised in that theluminescent material or other marker is of an organic nature and isprovided in form of a fluorescent material, comprising at least a hostlattice and an activator that is preferably present in ionic form, whichis responsible for the emitted wave image, in particular in form oflight.
 3. Filter element according to claim 1, characterised in that thehost lattice is made from oxidic materials, preferably Y₂O₃ orLu₃Al₅O₁₂, and that the materials used as activators are preferably rareearths and/or transition metals such as manganese, chromium or iron. 4.Filter element according to claim 1, characterised in that, in order toachieve a strong reflection on the surface of the respective elementcomponent, short-wave, in particular UV light is used, and for deepermaterial layers that are located below the surface, long-wave light, inparticular IR light is used.
 5. Filter element according to claim 1,characterised in that the short-wave light, which is invisible to thehuman eye, is absorbed by the respective element component and isre-emitted as long-wave light, which is visible to the human eye, orthat short-wave light is reflected that is detected by means of aspectroscopy method.
 6. Filter element according to claim 1,characterised that through a suitable choice of different activators akind of individual fingerprint is created for at least one type offilter element.
 7. Filter element according to claim 1, characterised inthat the activators are present in particle form in the size of <1 μm.8. Filter element according to claim 1, characterised in that thefluorescent material used is provided as a kind of ink or in an adhesive(27, 35), preferably mixed in form of a single or multiple-componentadhesive, with which the individual element components may at leastpartially be connected to each other and form the filter element. 9.Filter element according to claim 1, characterised in that the adhesive(27, 35), which contains the fluorescent material, serves the purpose toconnect the filter mat ends (30, 32) of the filter material (10) to eachother or to connect the filter material with at least one of the endcaps (26).
 10. Filter element according to claim 1, characterised inthat the individual filter folds (12) of the pleated filter material(10) are spaced and fixed in the adhesive bed (27) of the respective endcap (26) in such a way that an optical recognition of at least parts ofthe respective adhesive bed (27) between adjacent filter folds (12) ispossible.